Paper is conventionally manufactured by conveying a paper furnish, usually consisting of an initial slurry of cellulosic fibres, on a forming fabric or between two forming fabrics in a forming section, the nascent sheet then being passed through a pressing section and ultimately through a drying section of a papermaking machine. In the case of standard tissue paper machines, the paper web is transferred from the press fabric to a Yankee dryer cylinder then creped.
Paper machine clothing is essentially employed to carry the paper web through these various stages of the papermaking machine. In the forming section, the fibrous furnish is wet-laid onto a moving forming wire and water is encouraged to drain from it by means of suction boxes and foils. The paper web is then transferred to a press fabric that conveys it through the pressing section, where it usually passes through a series of pressure nips formed by rotating cylindrical press rolls. Water is squeezed from the paper web and into the press fabric as the web and fabric pass through the nip together. Press fabrics generally comprise a batt of fibres needled to a base fabric. In the final stage, the paper web is transferred either to a Yankee dryer, in the case of tissue paper manufacture, or to a set of dryer cylinders upon which, aided by the clamping action of the dryer fabric, the majority of the remaining water is evaporated.
The base fabrics of press felts are woven endless, whether they are seamed or not, such that the yarns of the weft in the loom lie in the machine direction of the fabric on the paper machine. The weft yarns weave back and forth continuously between the laterally extending edges of the fabric and form a seam loop at the reversals on one side. The two ends formed are then joined together on the machine by means of a pintle wire.
Press felts consist of multiple layers which are secured together by needling. This works by mechanically locking the constituent batt fibres into various layers and in so doing holds them together. In addition, the batt fibre gives a homogenous paper support surface. Due to the method of base fabric manufacture, the area around the seam is free of cross machine direction. (CD) yarns. This means that the ability of the batt fibre to become anchored in this region is much reduced, and the anchoring achieved much less effective than in the main area of the felt. Also, due to the greater void volume in the seam area, in comparison to the main body of the fabric, the propensity to marking of the paper sheet is greatly increased. In order to alleviate this problem a number of methods have been suggested in the prior art.
For example, in U.S. Pat. No. 5,476,123 (RYDIN), it is proposed to interweave an additional CD yarn between the pintle and the ends of the loops which is interlaced only with the upper passes of the loops. EP-A-1,233,103 (ALBANY) similarly discloses the provision of additional CD yarns woven in a leno weave with either the top or bottom layer of the seaming loops.
U.S. Pat. No. 5,799,709 (SHIPLEY) proposes the provision of an additional CD yarn between the last yarn of the main warp system and the pintle, which features relatively long floats over the top MD yarns, and interlacings with the lower MD yarns.
The Herring U.S. Pat. Nos. 6,267,150 and 6,273,146, similarly feature pairs of additional CD yarns inserted between the last standard warp yarn and seam loop with long floats over the top MD yarns, with alternatively spaced interlacings with the lower MD yarns. U.S. Pat. No. 6,289,940 (HERRING) and U.S. Pat. No. 6,318,413 (HERRING) feature additional CD yarns having more interlacings with the top layer than the lower layer, and also non interlaced portions within the loops. U.S. Pat. No. 6,273,147 (HERRING) shows a similar arrangement except for a different weave pattern. All the Herring US patents derive from the same group of provisional applications, and have similar disclosures.
U.S. Pat. No. 5,913,339 (LEE) features the provision of a pair of oppositely woven filler CD yarns between the last standard warp yarn and the pintle, where each filler yarn is interlaced with alternate upper and lower MD loop yarns.
U.S. Pat. No. 6,349,749 (QUIGLEY) features a weave pattern for the additional yarns similar to U.S. Pat. No. 6,289,940 (HERRING) mentioned above, but with one yarn woven preferentially with the top MD yarn layer and the other with the lower MD yarn layer.
In the above disclosures, it is to be noted that the additional cross machine direction yarns are inserted into the seam zone, after the last standard warp yarn, so that these yarns are the yarns which lie narest to the seam.
It has been found that such additional filler yarns tend to encroach into the seaming loops, as there is a tendency for them, due to low warp tension, to move laterally and become displaced towards the seaming zone, in turn causing an obstruction to pintle insertion and so making seaming increasingly more difficult. In addition, it has been found that seam loop distortion has also become an issue because of the fact that the additional binder yarns are woven in directly next to the seam loop.